Core Java Interview Questions with Answers

1. what is a transient variable?A transient variable is a variable that may not be serialized.2.which containers use a border Layout as their default layout?The window, Frame and Dialog classes use a border layout as their default layout.3.Why do threads block on I/O?Threads block on i/o (that is enters the waiting state) so that other threads may executewhile the i/oOperation is performed.4. How are Observer and Observable used?Objects that subclass the Observable class maintain a list of observers. When anObservable object isupdated it invokes the update() method of each of its observers to notify the observersthat it has changedstate. The Observer interface is implemented by objects that observe Observable objects.5. What is synchronization and why is it important?With respect to multithreading, synchronization is the capability to control the access ofmultiple threads toshared resources. Without synchronization, it is possible for one thread to modify ashared object whileanother thread is in the process of using or updating that object's value. This often leadsto significanterrors.6. Can a lock be acquired on a class?Yes, a lock can be acquired on a class. This lock is acquired on the class's Class object.7. What's new with the stop(), suspend() and resume() methods in JDK 1.2?The stop(), suspend() and resume() methods have been deprecated in JDK 1.2.8. Is null a keyword?The null value is not a keyword.9. What is the preferred size of a component?The preferred size of a component is the minimum component size that will allow thecomponent to displaynormally.10. What method is used to specify a container's layout?The setLayout() method is used to specify a container's layout.http://www.exforsys.com11. Which containers use a FlowLayout as their default layout?The Panel and Applet classes use the FlowLayout as their default layout.12. What state does a thread enter when it terminates its processing?When a thread terminates its processing, it enters the dead state.13. What is the Collections API?The Collections API is a set of classes and interfaces that support operations oncollections of objects.14. Which characters may be used as the second character of an identifier, but notas the firstcharacter of an identifier?The digits 0 through 9 may not be used as the first character of an identifier but they maybe used after thefirst character of an identifier.15. What is the List interface?The List interface provides support for ordered collections of objects.16. How does Java handle integer overflows and underflows?It uses those low order bytes of the result that can fit into the size of the type allowed bythe operation.17. What is the Vector class?The Vector class provides the capability to implement a growable array of objects18. What modifiers may be used with an inner class that is a member of an outerclass?A (non-local) inner class may be declared as public, protected, private, static, final, orabstract.19. What is an Iterator interface?The Iterator interface is used to step through the elements of a Collection.20. What is the difference between the >> and >>> operators?The >> operator carries the sign bit when shifting right. The >>> zero-fills bits that havebeen shifted out.21. Which method of the Component class is used to set the position and size of acomponent?setBounds()http://www.exforsys.com22. How many bits are used to represent Unicode, ASCII, UTF-16, and UTF-8characters?Unicode requires 16 bits and ASCII require 7 bits. Although the ASCII character set usesonly 7 bits, it isusually represented as 8 bits. UTF-8 represents characters using 8, 16, and 18 bit patterns.UTF-16 uses 16-bit and larger bit patterns.23What is the difference between yielding and sleeping?When a task invokes its yield() method, it returns to the ready state. When a task invokesits sleep()method, it returns to the waiting state.24. Which java.util classes and interfaces support event handling?The EventObject class and the EventListener interface support event processing.25. Is sizeof a keyword?The sizeof operator is not a keyword.26. What are wrapped classes?Wrapped classes are classes that allow primitive types to be accessed as objects.27. Does garbage collection guarantee that a program will not run out of memory?Garbage collection does not guarantee that a program will not run out of memory. It ispossible forprograms to use up memory resources faster than they are garbage collected. It is alsopossible forprograms to create objects that are not subject to garbage collection28. What restrictions are placed on the location of a package statement within asource code file?A package statement must appear as the first line in a source code file (excluding blanklines andcomments).29. Can an object's finalize() method be invoked while it is reachable?An object's finalize() method cannot be invoked by the garbage collector while the objectis still reachable.However, an object's finalize() method may be invoked by other objects.30. What is the immediate superclass of the Applet class?Panel31. What is the difference between preemptive scheduling and time slicing?http://www.exforsys.comUnder preemptive scheduling, the highest priority task executes until it enters the waitingor dead states ora higher priority task comes into existence. Under time slicing, a task executes for apredefined slice oftime and then reenters the pool of ready tasks. The scheduler then determines which taskshould executenext, based on priority and other factors.32. Name three Component subclasses that support painting.The Canvas, Frame, Panel, and Applet classes support painting.33. What value does readLine() return when it has reached the end of a file?The readLine() method returns null when it has reached the end of a file.34. What is the immediate superclass of the Dialog class?Window35. What is clipping?Clipping is the process of confining paint operations to a limited area or shape.36. What is a native method?A native method is a method that is implemented in a language other than Java.37. Can a for statement loop indefinitely?Yes, a for statement can loop indefinitely. For example, consider the following:for(;;) ;38. What are order of precedence and associativity, and how are they used?Order of precedence determines the order in which operators are evaluated inexpressions. Associatitydetermines whether an expression is evaluated left-to-right or right-to-left39. When a thread blocks on I/O, what state does it enter?A thread enters the waiting state when it blocks on I/O.40. To what value is a variable of the String type automatically initialized?The default value of an String type is null.41. What is the catch or declare rule for method declarations?If a checked exception may be thrown within the body of a method, the method musteither catch theexception or declare it in its throws clause.42. What is the difference between a MenuItem and a CheckboxMenuItem?http://www.exforsys.comThe CheckboxMenuItem class extends the MenuItem class to support a menu item thatmay be checked orunchecked.43. What is a task's priority and how is it used in scheduling?A task's priority is an integer value that identifies the relative order in which it should beexecuted withrespect to other tasks. The scheduler attempts to schedule higher priority tasks beforelower priority tasks.44. What class is the top of the AWT event hierarchy?The java.awt.AWTEvent class is the highest-level class in the AWT event-classhierarchy.45. When a thread is created and started, what is its initial state?A thread is in the ready state after it has been created and started.46. Can an anonymous class be declared as implementing an interface andextending a class?An anonymous class may implement an interface or extend a superclass, but may not bedeclared to doboth.47. What is the range of the short type?The range of the short type is -(2^15) to 2^15 - 1.48. What is the range of the char type?The range of the char type is 0 to 2^16 - 1.49. In which package are most of the AWT events that support the event-delegationmodel defined?Most of the AWT-related events of the event-delegation model are defined in thejava.awt.event package.The AWTEvent class is defined in the java.awt package.50. What is the immediate superclass of Menu?MenuItem51. What is the purpose of finalization?The purpose of finalization is to give an unreachable object the opportunity to performany cleanupprocessing before the object is garbage collected.52. Which class is the immediate superclass of the MenuComponent class.http://www.exforsys.comObject53. What invokes a thread's run() method?After a thread is started, via its start() method or that of the Thread class, the JVMinvokes the thread'srun() method when the thread is initially executed.54. What is the difference between the Boolean & operator and the && operator?If an expression involving the Boolean & operator is evaluated, both operands areevaluated. Then the &operator is applied to the operand. When an expression involving the && operator isevaluated, the firstoperand is evaluated. If the first operand returns a value of true then the second operandis evaluated. The&& operator is then applied to the first and second operands. If the first operandevaluates to false, theevaluation of the second operand is skipped.55. Name three subclasses of the Component class.Box.Filler, Button, Canvas, Checkbox, Choice, Container, Label, List, Scrollbar, orTextComponent56. What is the GregorianCalendar class?The GregorianCalendar provides support for traditional Western calendars.57. Which Container method is used to cause a container to be laid out andredisplayed?validate()58. What is the purpose of the Runtime class?The purpose of the Runtime class is to provide access to the Java runtime system.59. How many times may an object's finalize() method be invoked by the garbagecollector?An object's finalize() method may only be invoked once by the garbage collector.60. What is the purpose of the finally clause of a try-catch-finally statement?The finally clause is used to provide the capability to execute code no matter whether ornot an exception isthrown or caught.61. What is the argument type of a program's main() method?A program's main() method takes an argument of the String[] type.62. Which Java operator is right associative?The = operator is right associative.http://www.exforsys.com63. What is the Locale class?The Locale class is used to tailor program output to the conventions of a particulargeographic, political, orcultural region.64. Can a double value be cast to a byte?Yes, a double value can be cast to a byte.65. What is the difference between a break statement and a continue statement?A break statement results in the termination of the statement to which it applies (switch,for, do, or while).A continue statement is used to end the current loop iteration and return control to theloop statement.66. What must a class do to implement an interface?It must provide all of the methods in the interface and identify the interface in itsimplements clause.67. What method is invoked to cause an object to begin executing as a separatethread?The start() method of the Thread class is invoked to cause an object to begin executing asa separate thread.68. Name two subclasses of the TextComponent class.TextField and TextArea69. What is the advantage of the event-delegation model over the earlier eventinheritancemodel?The event-delegation model has two advantages over the event-inheritance model. First,it enables eventhandling to be handled by objects other than the ones that generate the events (or theircontainers). Thisallows a clean separation between a component's design and its use. The other advantageof the eventdelegationmodel is that it performs much better in applications where many events aregenerated. Thisperformance improvement is due to the fact that the event-delegation model does nothave to repeatedlyprocess unhandled events, as is the case of the event-inheritance model.70. Which containers may have a MenuBar?Frame71. How are commas used in the initialization and iteration parts of a for statement?Commas are used to separate multiple statements within the initialization and iterationparts of a forhttp://www.exforsys.comstatement.72. What is the purpose of the wait(), notify(), and notifyAll() methods?The wait(),notify(), and notifyAll() methods are used to provide an efficient way forthreads to wait for ashared resource. When a thread executes an object's wait() method, it enters the waitingstate. It only entersthe ready state after another thread invokes the object's notify() or notifyAll() methods.73. What is an abstract method?An abstract method is a method whose implementation is deferred to a subclass.74. How are Java source code files named?A Java source code file takes the name of a public class or interface that is defined withinthe file. A sourcecode file may contain at most one public class or interface. If a public class or interface isdefined within asource code file, then the source code file must take the name of the public class orinterface. If no publicclass or interface is defined within a source code file, then the file must take on a namethat is different thanits classes and interfaces. Source code files use the .java extension.75. What is the relationship between the Canvas class and the Graphics class?A Canvas object provides access to a Graphics object via its paint() method.76. What are the high-level thread states?The high-level thread states are ready, running, waiting, and dead.77. What value does read() return when it has reached the end of a file?The read() method returns -1 when it has reached the end of a file.78. Can a Byte object be cast to a double value?No, an object cannot be cast to a primitive value.79. What is the difference between a static and a non-static inner class?A non-static inner class may have object instances that are associated with instances ofthe class's outerclass. A static inner class does not have any object instances.80. What is the difference between the String and StringBuffer classes?String objects are constants. StringBuffer objects are not.81. If a variable is declared as private, where may the variable be accessed?http://www.exforsys.comA private variable may only be accessed within the class in which it is declared.82. What is an object's lock and which object's have locks?An object's lock is a mechanism that is used by multiple threads to obtain synchronizedaccess to the object.A thread may execute a synchronized method of an object only after it has acquired theobject's lock. Allobjects and classes have locks. A class's lock is acquired on the class's Class object.83. What is the Dictionary class?The Dictionary class provides the capability to store key-value pairs.84. How are the elements of a BorderLayout organized?The elements of a BorderLayout are organized at the borders (North, South, East, andWest) and the centerof a container.85. What is the % operator?It is referred to as the modulo or remainder operator. It returns the remainder of dividingthe first operandby the second operand.86. When can an object reference be cast to an interface reference?An object reference be cast to an interface reference when the object implements thereferenced interface.87. What is the difference between a Window and a Frame?The Frame class extends Window to define a main application window that can have amenu bar.88. Which class is extended by all other classes?The Object class is extended by all other classes.89. Can an object be garbage collected while it is still reachable?A reachable object cannot be garbage collected. Only unreachable objects may begarbage collected..90. Is the ternary operator written x : y ? z or x ? y : z ?It is written x ? y : z.91. What is the difference between the Font and FontMetrics classes?The FontMetrics class is used to define implementation-specific properties, such asascent and descent, of aFont object.92. How is rounding performed under integer division?http://www.exforsys.comThe fractional part of the result is truncated. This is known as rounding toward zero.93. What happens when a thread cannot acquire a lock on an object?If a thread attempts to execute a synchronized method or synchronized statement and isunable to acquirean object's lock, it enters the waiting state until the lock becomes available.94. What is the difference between the Reader/Writer class hierarchy and theInputStream/OutputStream class hierarchy?The Reader/Writer class hierarchy is character-oriented, and theInputStream/OutputStream class hierarchyis byte-oriented.95. What classes of exceptions may be caught by a catch clause?A catch clause can catch any exception that may be assigned to the Throwable type. Thisincludes the Errorand Exception types.96. If a class is declared without any access modifiers, where may the class beaccessed?A class that is declared without any access modifiers is said to have package access. Thismeans that theclass can only be accessed by other classes and interfaces that are defined within thesame package.97. What is the SimpleTimeZone class?The SimpleTimeZone class provides support for a Gregorian calendar.98. What is the Map interface?The Map interface replaces the JDK 1.1 Dictionary class and is used associate keys withvalues.99. Does a class inherit the constructors of its superclass?A class does not inherit constructors from any of its superclasses.100. For which statements does it make sense to use a label?The only statements for which it makes sense to use a label are those statements that canenclose a break orcontinue statement.101. What is the purpose of the System class?The purpose of the System class is to provide access to system resources.http://www.exforsys.com102. Which TextComponent method is used to set a TextComponent to the readonlystate?setEditable()103. How are the elements of a CardLayout organized?The elements of a CardLayout are stacked, one on top of the other, like a deck of cards.104. Is &&= a valid Java operator?No, it is not.105. Name the eight primitive Java types.The eight primitive types are byte, char, short, int, long, float, double, and boolean.106. Which class should you use to obtain design information about an object?The Class class is used to obtain information about an object's design.107. What is the relationship between clipping and repainting?When a window is repainted by the AWT painting thread, it sets the clipping regions tothe area of thewindow that requires repainting.108. Is "abc" a primitive value?The String literal "abc" is not a primitive value. It is a String object.109. What is the relationship between an event-listener interface and an eventadapterclass?An event-listener interface defines the methods that must be implemented by an eventhandler for aparticular kind of event. An event adapter provides a default implementation of an eventlistenerinterface.110. What restrictions are placed on the values of each case of a switch statement?During compilation, the values of each case of a switch statement must evaluate to avalue that can bepromoted to an int value.111. What modifiers may be used with an interface declaration?An interface may be declared as public or abstract.112. Is a class a subclass of itself?A class is a subclass of itself.http://www.exforsys.com113. What is the highest-level event class of the event-delegation model?The java.util.EventObject class is the highest-level class in the event-delegation classhierarchy.114. What event results from the clicking of a button?The ActionEvent event is generated as the result of the clicking of a button.115. How can a GUI component handle its own events?A component can handle its own events by implementing the required event-listenerinterface and addingitself as its own event listener.116. What is the difference between a while statement and a do statement?A while statement checks at the beginning of a loop to see whether the next loop iterationshould occur. Ado statement checks at the end of a loop to see whether the next iteration of a loop shouldoccur. The dostatement will always execute the body of a loop at least once.117. How are the elements of a GridBagLayout organized?The elements of a GridBagLayout are organized according to a grid. However, theelements are of differentsizes and may occupy more than one row or column of the grid. In addition, the rows andcolumns mayhave different sizes.118. What advantage do Java's layout managers provide over traditional windowingsystems?Java uses layout managers to lay out components in a consistent manner across allwindowing platforms.Since Java's layout managers aren't tied to absolute sizing and positioning, they are ableto accomodateplatform-specific differences among windowing systems.119. What is the Collection interface?The Collection interface provides support for the implementation of a mathematical bag -an unorderedcollection of objects that may contain duplicates.120. What modifiers can be used with a local inner class?A local inner class may be final or abstract.121. What is the difference between static and non-static variables?A static variable is associated with the class as a whole rather than with specific instancesof a class. Nonstaticvariables take on unique values with each object instance.http://www.exforsys.com122. What is the difference between the paint() and repaint() methods?The paint() method supports painting via a Graphics object. The repaint() method is usedto cause paint() tobe invoked by the AWT painting thread.123. What is the purpose of the File class?The File class is used to create objects that provide access to the files and directories of alocal file system.124. Can an exception be rethrown?Yes, an exception can be rethrown.125. Which Math method is used to calculate the absolute value of a number?The abs() method is used to calculate absolute values.126. How does multithreading take place on a computer with a single CPU?The operating system's task scheduler allocates execution time to multiple tasks. Byquickly switchingbetween executing tasks, it creates the impression that tasks execute sequentially.127. When does the compiler supply a default constructor for a class?The compiler supplies a default constructor for a class if no other constructors areprovided.128. When is the finally clause of a try-catch-finally statement executed?The finally clause of the try-catch-finally statement is always executed unless the threadof executionterminates or an exception occurs within the execution of the finally clause.129. Which class is the immediate superclass of the Container class?Component130. If a method is declared as protected, where may the method be accessed?A protected method may only be accessed by classes or interfaces of the same package orby subclasses ofthe class in which it is declared.131. How can the Checkbox class be used to create a radio button?By associating Checkbox objects with a CheckboxGroup.132. Which non-Unicode letter characters may be used as the first character of anidentifier?http://www.exforsys.comThe non-Unicode letter characters $ and _ may appear as the first character of anidentifier133. What restrictions are placed on method overloading?Two methods may not have the same name and argument list but different return types.134. What happens when you invoke a thread's interrupt method while it issleeping or waiting?When a task's interrupt() method is executed, the task enters the ready state. The nexttime the task entersthe running state, an InterruptedException is thrown.135. What is casting?There are two types of casting, casting between primitive numeric types and castingbetween objectreferences. Casting between numeric types is used to convert larger values, such asdouble values, tosmaller values, such as byte values. Casting between object references is used to refer toan object by acompatible class, interface, or array type reference.136. What is the return type of a program's main() method?A program's main() method has a void return type.137. Name four Container classes.Window, Frame, Dialog, FileDialog, Panel, Applet, or ScrollPane138. What is the difference between a Choice and a List?A Choice is displayed in a compact form that requires you to pull it down to see the listof availablechoices. Only one item may be selected from a Choice. A List may be displayed in such away that severalList items are visible. A List supports the selection of one or more List items.139. What class of exceptions are generated by the Java run-time system?The Java runtime system generates RuntimeException and Error exceptions.140. What class allows you to read objects directly from a stream?The ObjectInputStream class supports the reading of objects from input streams.141. What is the difference between a field variable and a local variable?A field variable is a variable that is declared as a member of a class. A local variable is avariable that isdeclared local to a method.http://www.exforsys.com142. Under what conditions is an object's finalize() method invoked by the garbagecollector?The garbage collector invokes an object's finalize() method when it detects that the objecthas becomeunreachable.143. How are this() and super() used with constructors?this() is used to invoke a constructor of the same class. super() is used to invoke asuperclass constructor.144. What is the relationship between a method's throws clause and the exceptionsthat can bethrown during the method's execution?A method's throws clause must declare any checked exceptions that are not caught withinthe body of themethod.145. What is the difference between the JDK 1.02 event model and the eventdelegationmodelintroduced with JDK 1.1?The JDK 1.02 event model uses an event inheritance or bubbling approach. In this model,components arerequired to handle their own events. If they do not handle a particular event, the event isinherited by (orbubbled up to) the component's container. The container then either handles the event orit is bubbled up toits container and so on, until the highest-level container has been tried.In the event-delegation model, specific objects are designated as event handlers for GUIcomponents.These objects implement event-listener interfaces. The event-delegation model is moreefficient than theevent-inheritance model because it eliminates the processing required to support thebubbling of unhandledevents.146. How is it possible for two String objects with identical values not to be equalunder the ==operator?The == operator compares two objects to determine if they are the same object inmemory. It is possible fortwo String objects to have the same value, but located indifferent areas of memory.147. Why are the methods of the Math class static?So they can be invoked as if they are a mathematical code library.http://www.exforsys.com148. What Checkbox method allows you to tell if a Checkbox is checked?getState()149. What state is a thread in when it is executing?An executing thread is in the running state.150. What are the legal operands of the instanceof operator?The left operand is an object reference or null value and the right operand is a class,interface, or array type.151. How are the elements of a GridLayout organized?The elements of a GridBad layout are of equal size and are laid out using the squares of agrid.152. What an I/O filter?An I/O filter is an object that reads from one stream and writes to another, usuallyaltering the data in someway as it is passed from one stream to another.153. If an object is garbage collected, can it become reachable again?Once an object is garbage collected, it ceases to exist. It can no longer become reachableagain.154. What is the Set interface?The Set interface provides methods for accessing the elements of a finite mathematicalset. Sets do notallow duplicate elements.155. What classes of exceptions may be thrown by a throw statement?A throw statement may throw any expression that may be assigned to the Throwabletype.156. What are E and PI?E is the base of the natural logarithm and PI is mathematical value pi.157. Are true and false keywords?The values true and false are not keywords.158. What is a void return type?A void return type indicates that a method does not return a value.159. What is the purpose of the enableEvents() method?http://www.exforsys.comThe enableEvents() method is used to enable an event for a particular object. Normally,an event is enabledwhen a listener is added to an object for a particular event. The enableEvents() method isused by objectsthat handle events by overriding their event-dispatch methods.160. What is the difference between the File and RandomAccessFile classes?The File class encapsulates the files and directories of the local file system. TheRandomAccessFile classprovides the methods needed to directly access data contained in any part of a file.161. What happens when you add a double value to a String?The result is a String object.162. What is your platform's default character encoding?If you are running Java on English Windows platforms, it is probably Cp1252. If you arerunning Java onEnglish Solaris platforms, it is most likely 8859_1..163. Which package is always imported by default?The java.lang package is always imported by default.164. What interface must an object implement before it can be written to a streamas an object?An object must implement the Serializable or Externalizable interface before it can bewritten to a stream asan object.165. How are this and super used?this is used to refer to the current object instance. super is used to refer to the variablesand methods of thesuperclass of the current object instance.166. What is the purpose of garbage collection?The purpose of garbage collection is to identify and discard objects that are no longerneeded by a programso that their resources may be reclaimed and reused.167. What is a compilation unit?A compilation unit is a Java source code file.168. What interface is extended by AWT event listeners?All AWT event listeners extend the java.util.EventListener interface.http://www.exforsys.com169. What restrictions are placed on method overriding?Overridden methods must have the same name, argument list, and return type. Theoverriding method maynot limit the access of the method it overrides. The overriding method may not throwany exceptions thatmay not be thrown by the overridden method.170. How can a dead thread be restarted?A dead thread cannot be restarted.171. What happens if an exception is not caught?An uncaught exception results in the uncaughtException() method of the thread'sThreadGroup beinginvoked, which eventually results in the termination of the program in which it is thrown.172. What is a layout manager?A layout manager is an object that is used to organize components in a container.173. Which arithmetic operations can result in the throwing of anArithmeticException?Integer / and % can result in the throwing of an ArithmeticException.174. What are three ways in which a thread can enter the waiting state?A thread can enter the waiting state by invoking its sleep() method, by blocking on I/O,by unsuccessfullyattempting to acquire an object's lock, or by invoking an object's wait() method. It canalso enter thewaiting state by invoking its (deprecated) suspend() method.175. Can an abstract class be final?An abstract class may not be declared as final.176. What is the ResourceBundle class?The ResourceBundle class is used to store locale-specific resources that can be loaded bya program totailor the program's appearance to the particular locale in which it is being run.177. What happens if a try-catch-finally statement does not have a catch clause tohandle anexception that is thrown within the body of the try statement?The exception propagates up to the next higher level try-catch statement (if any) orresults in the program'stermination.178. What is numeric promotion?http://www.exforsys.comNumeric promotion is the conversion of a smaller numeric type to a larger numeric type,so that integer andfloating-point operations may take place. In numerical promotion, byte, char, and shortvalues areconverted to int values. The int values are also converted to long values, if necessary.The long and floatvalues are converted to double values, as required.179. What is the difference between a Scrollbar and a ScrollPane?A Scrollbar is a Component, but not a Container. A ScrollPane is a Container. AScrollPane handles itsown events and performs its own scrolling.180. What is the difference between a public and a non-public class?A public class may be accessed outside of its package. A non-public class may not beaccessed outside ofits package.181. To what value is a variable of the boolean type automatically initialized?The default value of the boolean type is false.182. Can try statements be nested?Try statements may be tested.183. What is the difference between the prefix and postfix forms of the ++ operator?The prefix form performs the increment operation and returns the value of the incrementoperation. Thepostfix form returns the current value all of the expression and then performs theincrement operation onthat value.184. What is the purpose of a statement block?A statement block is used to organize a sequence of statements as a single statementgroup.185. What is a Java package and how is it used?A Java package is a naming context for classes and interfaces. A package is used tocreate a separate namespace for groups of classes and interfaces. Packages are also used to organize relatedclasses and interfacesinto a single API unit and to control accessibility to these classes and interfaces.186. What modifiers may be used with a top-level class?A top-level class may be public, abstract, or final.http://www.exforsys.com187. What are the Object and Class classes used for?The Object class is the highest-level class in the Java class hierarchy. The Class class isused to representthe classes and interfaces that are loaded by a Java program.188. How does a try statement determine which catch clause should be used tohandle an exception?When an exception is thrown within the body of a try statement, the catch clauses of thetry statement areexamined in the order in which they appear. The first catch clause that is capable ofhandling the exceptionis executed. The remaining catch clauses are ignored.189. Can an unreachable object become reachable again?An unreachable object may become reachable again. This can happen when the object'sfinalize() method isinvoked and the object performs an operation which causes it to become accessible toreachable objects.190. When is an object subject to garbage collection?An object is subject to garbage collection when it becomes unreachable to the program inwhich it is used.191. What method must be implemented by all threads?All tasks must implement the run() method, whether they are a subclass of Thread orimplement theRunnable interface.192. What methods are used to get and set the text label displayed by a Buttonobject?getLabel() and setLabel()193. Which Component subclass is used for drawing and painting?Canvas194. What are synchronized methods and synchronized statements?Synchronized methods are methods that are used to control access to an object. A threadonly executes asynchronized method after it has acquired the lock for the method's object or class.Synchronizedstatements are similar to synchronized methods. A synchronized statement can only beexecuted after athread has acquired the lock for the object or class referenced in the synchronizedstatement.http://www.exforsys.com195. What are the two basic ways in which classes that can be run as threads may bedefined?A thread class may be declared as a subclass of Thread, or it may implement theRunnable interface.196. What are the problems faced by Java programmers who don't use layoutmanagers?Without layout managers, Java programmers are faced with determining how their GUIwill be displayedacross multiple windowing systems and finding a common sizing and positioning thatwill work within theconstraints imposed by each windowing system.197. What is the difference between an if statement and a switch statement?The if statement is used to select among two alternatives. It uses a boolean expression todecide whichalternative should be executed. The switch statement is used to select among multiplealternatives. It usesan int expression to determine which alternative should be executed.198. What is the List interface?The List interface provides support for ordered collections of objects.